Double antibody radioimmunoassay methods were developed for the determination of baboon luteinizing hormone (bLH) and follicle stimulating hormone (bFSH). The bLH radioimmunoassay employs a unique anti-ovine LH serum (GDN-15) and ovine LH (LER-1056-C2) for radioiodination, while the bFSH radioimmunoassay employs an heterologous system, i.e., an anti-ovine FSH serum (H-31) and purified human FSH for radioiodination. The reference standard used in both assays is a crude rhesus pituitary extract (LER-1909-2). Elevated endogeneous baboon plasma TSH and prolactin induced by the intravenous administration of 500 microgram of TRH had no influence on the levels of LH and FSH, whereas simultaneous intravenous administration of 100 microgram LHRH and 500 microgram TRH raised the levels of LH and FSH in plasma. hPRL, hCG, hTSH and hGH did not cross react with either the bLH or the bFSH assay system. The determination of plasma LH and FSH concentrations in daily samples from 6 mature female baboons throughout ovulatory menstrual cycles revealed patterns qualitatively similar to those of the rhesus monkey and human females.